This invention relates to a recording/reproducing method and device for controlling sound emission for an automatic performing piano, and more specifically to such a piano which is immune from inaccuracy of performance in sound reproduction due to the time lag of emission of sound caused by variations in intensity of depressed keys.
A conventional automatic performing piano has suffered from imbalance of sound emission timing between strong key strokes and weak key strokes. This is due to the time period from a depress-key command (on-event) to actual emission of sound during which a solenoid is energized.
Some prior art methods try to solve this problem by adopting a sound prohibited time period T.sub.1, as shown in FIG. 11, in designing the value of electric power L.sub.drv to be supplied to the solenoid for the depressed keys. In the figure, L.sub.1 is an original voltage level, L.sub.2 is a start-up voltage level, and L.sub.3 is a holding voltage level. T.sub.2 is a time period to sustain the start-up voltage level. The sound prohibited time period T.sub.1 is provided at the first stage of the application of electric power L.sub.drv in order to correct emission timing. The sound prohibited time period T.sub.1 is determined according to depression intensity data included in depression data, such that the stronger the key stroke is, the longer the duration of the sound prohibited time period T.sub.1. The maximum value of the sound prohibited time period T.sub.1 is 100 milliseconds.
In formulating or formatting recorded performance information to be later reproduced, the prior art methods and devices define the occurrence of an on-event and off-event as the timing of depression and release of a key, respectively, which are detected by key sensors 7 and 8 shown in FIG. 3. However, this method suffers from the following problem.
Since hammer systems and other mechanisms respond to strong key strokes more quickly than to weak key strokes as shown in FIG. 12A and FIG. 12B, a time period of emission delay in recording TD.sub.rec-on, which is the time lag between occurrence of an on-event t.sub.on and actual sound emission t.sub.music, shortens as the key stroke intensifies. Therefore, in recording an original performance by a performer, simultaneous occurrence of an on-event for a strong key stroke and a weak key stroke must be interpreted in actual sound emission as a strong key stroke followed by a weak key stroke as shown in FIG. 12C to reproduce the performance with fidelity and accuracy. The prior art method and device thus fails to reproduce performance with high fidelity and accuracy because of the definition of an on-event and an off-event as the actual timing of depression and release of key, respectively.
Moreover, the following problem occurs in determining the sound prohibited time period T.sub.1 simply according to depression intensity in designing a chart or amount of electric power L.sub.drv for the performance information thus recorded. Since recording is executed according to the occurrence timing of on-event shown in the graph of FIG. 13, but not to the actual and acoustic or sound emission timing shown in the second graph of FIG. 13, the recorded interval of emission INT.sub.rec between a strong key stroke and an immediately following weak key stroke is shorter than the actual interval of emission INT.sub.act.
Further, by providing the sound prohibited time period T.sub.1 again in the sound reproduction steps, the reproduced interval of emission between the two key strokes is further shortened as shown in the fourth and fifth graphs of FIG. 13. Consequently, the time period for holding emission of the former of two successive key strokes may be corroded and shortened by the sound prohibited time period T.sub.1 for the latter, occasionally resulting in failure to reproduce the sound for the former key stroke.